1. Field of the Invention
This invention generally relates to a metallic seal for creating a seal between a pair of members. More specifically, the present invention relates to a seal that provides a highly reliable seal by concentrating the available load over a narrow band (small sealing area equaling high contact stress) to produce a high quality sealing dam over a sufficient width to minimize leakage on a molecular level.
2. Background Information
A typical static seal assembly has a first member with a first mating surface, an annular seal of suitable sealing material (e.g., metal O-ring), and a second member with a second mating surface. A mechanical load is applied to the seal through the first and second mating surfaces of the members. Typically, the mechanical load is created by torquing down a multitude of fasteners such that a displacement, also known as compression, occurs between the sealing surfaces. The net loading of the contact surfaces creates the two sealing dams.
The low leakage requirement can be achieved by compressing a solid metal ring of rectangular cross-section with a sufficient force. One problem with a solid metal ring is that the force created could be of sufficient magnitude to cause plastic deformation of the mating surfaces of the members. This plastic deformation of the mating surface is called brinelling. Once brinelled, the probability of proper resealing is drastically reduced without first repairing the damaged sealing surfaces.
The design requirements for static sealing therefore requires an optimum load level and flexibility. A good static seal when compressed must be able to generate load levels large enough to seal, but not large enough to brinell the cavity surfaces. Currently, there are many types of metallic seals in the prior art.
The metallic “O” rings were an early effort to meet these conflicting design requirements. However, the resiliency of this type of seal is rather limited because the “O” ring, whether solid or hollow, is usually too stiff, and is inherently expensive. The development of the C-shaped seal was an improvement to the “O” ring. In particular, by simply discarding a portion of the “O”, the hoop restraint of the seal is greatly reduced and the seal becomes more flexible. However, the basic “C” seals typically cannot reach the desirable standard vacuum level of 1×10e−9 cc/sec He leakage rate or better without modification and without being coated with very soft plating materials. Some previous C-shaped seals have been designed to provide this level of seal integrity.
In addition to typical “C” seals, other prior seals include spring-energized “C” seals, spring-energized “C” seals with triangular feature (Delta-seal), deformable metallic gaskets, E-seals with single or multiple convolutions. Some of these previous designs can provide the level of seal integrity provided by the disclosed device at comparable load levels or physical restraints.
Examples of these prior sealing rings are disclosed in U.S. Pat. No. 4,813,692 and U.S. Pat. No. 4,854,600. However, the seals of these two patent address semi-dynamic applications where the two sealing surfaces are moving relative to each other. These patents are associated with larger cross sections and the method of deformation uses both axial bending and torsion.
In view of the above, it will be apparent to those skilled in the art that there exists a need for improved metallic sealing rings with optimized sealing areas that can be used at high temperatures and pressures while providing high reliability and pressure tight sealing. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art once given this disclosure.